Axial blower



- April 13, 1943. H. PFENI\IIINGER I AXIAL BLOWER Filed Feb. 2, 1942 Patented Apr. 13, 1943 AXIALBLOWER Hans Pi'enninger, Wcttingen, Switzerland assignor to Aktiengesellschait Brown, Boverie & Ole,

Baden, Switzerland Application February 2, 1942, Serial No. 429,329 In Switzerland December 9, 1940 7 Claims. (Cl.230-1Ll5 It is known'that axial or helical blowers begin to pump or surge as soon as the quantity drawn in by suction falls below the minimum delivery quantity given for any speed of revolution by the characteristic curve of the blower. The pumping or surging can be prevented by delivering a larger quantity than corresponds to this minimum and blowing oi! the excess. In order that the expenditure 'of work for the excess quantity delivered may not be entirely wasted, this excess is caused to perform work by passin it into a turbine, which is usually lodged in the suction chamber of the blower and is connected by separate pipes with the delivery connection of the blower. That these recovery turbines, hitherto adopted almost exclusively in radial (centrifugal) blowers, have not a very high eiliciency, is of subordinate importance, since centrifugal blowers admit of comparatively large diminutions of the normal suction quantity, so the blowing oil is not required until a late stage. and in addition to this these diminutions of delivery in centrifugal blowers also admit of bein economically obtained by throttling on the suction side.

The conditions are diflferent in the case of the axial compressor. is substantially steeper than that of the radial compressor, that is to say, at a constant speed it approaches the pumping limit more rapidly, its regulation by throttling on the suction side is very uneconomical, whereas the blowing of! on the delivery side is associated with substantially lower losses than the blowing oi! or the throttling in radial compressors.

In connection with a recovery turbineof good efficiency, therefore, protection against pumping by blowing oil must yield an economical method of operation in axial compressors. It has intact been found that the same admits of being designed so economically that it can be employed not merely as an incidental precaution for guarding against pumping but as a normal regulating device for axial blowers- A presumption is, he ver, having regard to the restrictedpres'suie drop available for the turbine,

that everything should be avoided that would impair the recovery'of the work 'of compression expended upon the quantity to be blown on.

Now the subject of the present invention is an axial blower with a drum as runner, in which, for regulating purposes, a portion of the compressed fluid is branched of! and led to a turbine mounted upon the same shaft, and both the turbine and the inlet for the fluid flowing away Its characteristic curve T to the turbine are so arranged that the fluid can flow from the blower to the turbine directly, that is to say, without any considerable changes 01' direction and without leaving the common casing. 4

The invention is illustrated by way of example in the accompanying drawing, in which Figure 1 is a diagrammatic view of such a blower in axial section;

Figures 2, 3 and 4 are fragmentary axial sec tions on a larger scale showing three diilferent forms of construction of the adjustable guide blades; I

Figures 2a, 3a and 4a-are fragmentary transverse sections through the blades of the embodiments shown in Figures 2, 3 and 4, respectively; and

Figure 5 shows a blower with drums of different diameters;

In Figure 1, I denotes the common casing, 2 the common drum; and 3 the blading of the compressor, while 4 is the blading of the gas turbine. The main portion or the compressed fluid leaves the blower by way of a diffuser-like expansion 5 and through a-pipe connection 6. Part of the fluid passes directly, that is, without substantial deflection and without leavin the casing I, to the first ring of guide blades 1 of the turbine. After expansion with performance of work this portion of the fluid leaves the casing at 8. 9 is a motor or engine for driving the blower. I

Designers have hitherto contented themselves with regulating the quantity of air flowing away to the turbine by means of simple lift valves or slide valves, leaving the cross-sectional areas of passage of the first ring of guide blades unaltered. In this way a large portion of the available energy was wasted by throttling losses; 'According to this invention, however, these losses are obviated byeilecting the regulating of the quantity delivered by means or pivoted guideblades in a manner known in itself. The guide blades 1 are therefore rotatable, and may be provided, as shown in Figure -2,with any convenient adjusting means known in'itself. These guide blades may also advantageously be made in two parts, one of which is fixed and the other rotatable. Figures 3 and 4 show two constructional examples of this. In Figure 3 the actual guide blade III is rotatable, but the preceding blade l2, which serves to carry labyrinth packing II, is stationary. In Figure 4 the guide blade I! is stationary, whilethe leading or preparatory blade l4 can be turned so far as to provide a complete closure.

To enable the regulating to be effected continuously the adjustable blades are divided up into a number of groups, which can be actuated separately, and the internal cross-sectional areas of which increase in geometrical progression. By appropriately grouping these groups of nozzles of different sizes an almost constant increase of are provided for instance in turbines in which a large proportion of the fall of pressure is already converted into work in the first ring of guide blades. The reference numerals denote the same parts in this figure as in Figures 1 and 3. What is different is the drum, the diameter of which is greater in the turbine part i5 than in the compressor part i6.

I claim:

1. An axial flow blower comprising an impeller drum, a turbine mounted on the same shaft as the impeller drum, and means for the flow of fluid from the impeller drum to a point of use including a branch ior the fiow of part of the fluid directly from the impeller drum to said turbine without substantial change of direction.

2. An axial flow blower comprising an impeller drum, a turbine mounted on the same shaft as the impeller drum, a common casing for said impeller drum and said turbine, and means for the flow of fluid from the impeller drum to a point of use including a branch for the flow of part of the fluid directly from the impeller drum to said turbine without substantial change of direction and without leaving the common casing.

3. An axial flow blower as defined in claim 2 wherein the blading of the impeller and the blading of the turbine are mounted on the same drum.

4. An axial flow blower as defined in claim 2 wherein the blading of the impeller and the blading of the turbine are mounted on the same drum, the diameter of the portion of the drum carrying the impeller blades and the diameter of the portion of the drum carrying the turbine blades being so related that the residual axial thrusts are counterbalanced by the pressures upon the end faces of the drum.

5. An axial flow blower as defined in claim 2 wherein the blades of the first guide ring of the turbine are adjustable for regulating the quantity of fluid passing through said branch,

6. An axial flow blower as defined in claim 2 wherein the blades in the first guide ring of the turbine comprise two sets of blades, one of which is rotatable for regulating the quantity of fluid passing through said branch and the other of which is stationary.

'1. An axial flow blower as defined in claim 2, wherein the blades of the first guide ring of the turbine are adjustable for regulating the quantity of fluid passing through said branch, said adjustable guide blades being divided into separately actuatable groups, the cross-sectional areas of passage provided by said groups increasing from group to group in geometrical progression.

HANS PFENNINGER. 

